Various methods of wellbore isolation, screen filtration, and production control are known in the art, including applications in the field of oil and gas exploitation. In the past, the annular space in a borehole, outside the screen of a tubing string, was filled with gravel to prevent the production of undesirable sand and other fines from a formation. More recently, with the advent of tubular expansion technology, it was thought that the need for gravel packing could be eliminated if the screen could be expanded in place to eliminate the surrounding annular space that had heretofore been packed with gravel. Problems arose with the screen expansion technique as a replacement for gravel packing because of wellbore shape irregularities. Subsequently, therefore, the use of conformable materials for such applications have been disclosed. The conformable material, in the form of an annular layer around the screen or other support of a tubing string, expands sufficiently after being run into the wellbore in order to contact the wellbore and fill the surrounding annulus. For example, various screen assemblies have been designed with an outer layer that can conform to the borehole shape upon expansion. Such designs are described in U.S. Patent Pub. 2009/0130938; U.S. Pat. No. 7,318,481; and US Patent Pub. 2010/0089565. In one embodiment, a material is selected that will expand after being contacted with wellbore fluids.
Self-conforming expandable screens comprising thermosetting open-cell shape-memory polymeric foam have been disclosed. Shape-memory materials are materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape induced by an external stimulus or trigger. The shape memory effect of these materials can be triggered, for example, by temperature change, an electric or magnetic field, light, change in pH, or other means. Shape-memory materials typically comprise viscoelastic polymers that can exist in two distinct states, exhibiting either the properties of a glass (high modulus) or those of a rubber (low modulus).
Mechanical and filtration properties of the conformable material, capable of screening production flow, strongly depends on the microcellular structure, including average cell size. Such properties can also depend on pore throat geometry. One method of providing a microcellular structure is by foaming a polymer. However, controlling a foaming process has been difficult and unpredictable. Thus, there is a need for an improved method of preparing a foamed conformable material having a desired pre-designed microcellular structure.
It would be very desirable and important to discover a method for preparing a foamed microcellular conformable material that can be deployed as an element at a particular location downhole in a wellbore, which material can achieve desired conformability and screening filtration for wellbore isolation and production control. Generally, greater versatility for such materials and their method of production is desired, as this provides more flexibility in screen assembly designs and provides the operator more flexibility in designing their placement and configuration for use in wellbores.
These and other advantages of the present invention will become more apparent to one skilled in the art from a review of the description of the preferred embodiment and the claims that appear below.